Amplifying system



VJuly 29, 1941. v. Mls'rRo AMPLIFYING SYSTEM Filed sept. 22, 1938 3Sheets-Sheet July 29, 1941. v. MlsTRo AMPLIFYING SYSTEM Filed Sept. 22,1938 s sheets-sheet 2 July 29, 1941. v. MIsTRo AMPLIFYING SYSTEM FiledSept. 22, 1938 3 Sheets-Sheet 3 dezzozf? 'cmzls/Zfo Patented July 29,1941 10 Claims.

My invention relates to amplifying systems, and more particularly tosuch systems having high gain and utilized for amplifying impulses forsuch purposes as studying Wave forms where iidelity and constancy ofoperation are particularly desirable.

The ampliiication and study of very small electrical impulses and wavesthat are generated or controlled by the actions of certain parts of thehuman anatomy has become an adjunct to medical science. Because of theminuteness of the energy or potentials to be amplified, high gains inboth potential and power are required, particularly Where a recordingdevice is actuated from the output of the amplier. The actuation of arecording device is very desirable in such work for the preservation andstudy of the results and to facilitate correlation of the results withother events. Also, fidelity and the practical elimination of thegeneration of impulses within the amplifier, or amplification of outsidedisturbances are very important in obtaining consistent and usableresults.

To improve the portability of the apparatus and eliminate the carerequired by storage batteries, it is desirable that as much of theapparatus as possible be energized from an alternating current source.However, the requirements of fidelity and constancy of amplifieroperation without regeneration make special precautions necessary inutilizing alternating current mains as a power source. Theserequirements also, when considered from the standpoint 0f economics,make the judicious selection of power sources for various circuits anadditional problem.

Although not limited to uses related to medical science, the amplifyingsystem of my invention, which is disclosed herein, is particularlyadapted to the amplication of electrical impulses cr Waves obtained fromthe human anatomy, such as from electrodes applied to different parts ofthe head. With such use in mind, particular attention has been paid tothe judicious selection of power sources and features of design whichare consistent with necessary factors, such as high gain, delity,constancy of operation, freedom from disturbances from outside theamplifier and generated within the amplifier, as well as portability.

It is, therefore,y an object of my invention to provide an amplifyingsystem adapted to be used for the amplification and recording ofelectrical impulses or waves obtained from parts of the anatomy.

Another object of my invention is to provide an amplifying system whichincludes a multistage, high gain amplifier in which the higher voltagesand filament heating voltages are obtained from the alternating currentmains and a voltage regulating means for minimizing the effect ofvariations of voltage of the mains upon the output of the amplier.

Another object of my invention is to provide a high gain multi-stageamplifier including means for preventing oscillation of the amplifiertubes and the consequent generation of waves or impulses within theamplifier itself. In accordance with my invention, this object isaccomplished by the connecting of resistors' in series With the controlgrids of certain of the amplifier tubesin addition to dividing theamplier into separately shielded sections and separating and shieldingthe power supply means for the separate sections.

Another object of my invention is to provide an amplifying systemincluding stages of the push-pull type and means for balancing the loadon the tubes of the push-pull stages. In the disclosed embodiment of myinvention this object is accomplished by the provision of an indicatingdevice or meter in the output circuit of the last push-pull stage, avariable resistance unit for balancing the load on the vacuum tubes ofthe said last push-pull stage and a'variable resistance unit forsubsequently balancing the input to the preceding push-pull stage; theproper balancing of the output from the last push-pull stage and inputto the preceding push-pull stage being indicated by the indicatingdevice.

Another object of my invention is to provide a voltage regulating systemparticularly adapted for use in connection With an amplifier system andwhich includes aninstrumentalty providing a partial regulation of thevoltage and means in addition to the said instrumentality for providinga more precise regulation of the voltage. In the disclosed embodiment ofmy invention a gas discharge tube is utilized to provide the partialregulation of the rectified alternating current voltage and a pair ofcooperating vacuum tubes provide the more precise regulation thereof.

Another object of my invention is to provide an amplifying systemincluding a voltage regulator having gas discharge and vacuum tubecontrol instrumentalities and a cooperating circuit including resistorsfor stabilizing high voltages utilized in the amplifier. Y

Another object of my invention is to provide-an amplifying systemincluding separatelyshielded connected sections, each of which sectionsincludes one or more amplifying stages and some of which sectionsinclude Voltage regulating means for stabilizing voltages utilized inthe stage or stages within the same section.

Another object of my invention is to provide an amplifying systemcomprehending a push-pull type amplifying stage and a power supplycircuit therefor including a voltage regulator tube for regulating theanode potential of each of the push-pull amplifier tubes and a variableimpedance element for balancing or controlling the current flow throughthe voltage regulator tubes.

The foregoing, together with further objects, features and advantages ofmy invention are set forth in the following description of a specicembodiment thereof illustrated in the accompanying drawings wherein:

Figs. 1, 2 and 3 are circuit diagrams of sectional parts of anamplifying system which constitutes a preferred embodiment of myinvention. Figure 1A is a preferred form of connector adapted to beutilized with the disclosed circuit diagrams. Having general referenceto the drawings, the amplifying system of my invention is preferablydivided into sections which are separately shielded, as indicated by thedotted lines at I in Fig. l, II in Fig. 2, and I2 in Fig. 3.

A rst stage I3 of the amplifier which is enclosed in the shield I9 andshown in Fig. 1, preferably constitutes the first section and is of theresistance coupled push-pull type. The second section, which is shown inFig. 2, preferably includes two resistance coupled stages I4 and I5connected in cascade and enclosed in the shield II. The third section,shown in Fig. 3, preferably includes a resistance coupled push-pullstage I6, which is enclosed in the shield I2. The stages in the sectionsshown in Figs. 1, 2 and 3 are adapted to be connected in cascade, aswill be more fully described.

With particular reference to Fig. l, Vacuum amplifier tubes I1 and I8,respectively, include anodes or plates I9 and 20, control grids 2I and22, screen grids 23 and 24, cathodes 25 and 26, and heaters 21 and 28.The heaters 21 and 28 are connected in parallel and a transformer 29 isconnected thereacross to energize or heat the heaters. The transformer29 has a primary Winding 30 that is connected to line terminals 3| and32 which are adapted to be connected i to alternating current mains andhas a secondary Winding 33 connected across the heaters 21 and 28. Thistransformer 29 is preferably individually shielded by a shield 34. Thecontrol grids 2I and 22 are connected across a resistor 35 and arerespectively connected to input terminals 36 and 31 which are preferablyspring contacts of a jack 38, which jack has another contact element 39that is grounded at 49.

The anodes or plates I9 and 20 are connected together through anode orplate coupling resistors 4I and 42 and are respectively connectedthrough condensers 43 and 44 to output terminals 45 and 46, which larepreferably the tip and ring elements of a jack. The mid-tap or commonconnection of the resistors 4I and 42 is connected to the positiveterminal of a battery 41, the negative terminal of the battery 41 beingconnected to the cathodes 25 and 26 so that the anode potential isprovided thereby.

The screen grids 23 and 24 are connected to a tap 48 on the battery 41to establish their potential. A battery 49 having one terminal connectedto the cathodes 25 and 26 and the other terminal connected to a variablemid-tap 50 on the resistor 35 provides a biasing potential for the grids2I and 22. The cathodes 25 and 26 are also connected through a resistor5I to the output terminal or ring 46. The output terminal or ring 43 isalso preferably grounded at 52.

A plug 53, shown in Fig. 1A, is provided for making input connectionsthrough the contacts 36 and 31 of the jack 38 to the grids 2| and 22.This plug 53 has a ring or Contact element 54 that is adapted to contactthe spring 31 and a tip or contact element 55 that is adapted to engagethe contact 35. The ring 54 and tip 55 are connected to suitableconnecting leads 56 and 51, which are preferably shielded as indicatedat 58 and serve to make connection to suitable electrodes or signalinput contacts. As a further precaution to prevent the pick-up of straysignals or disturbances, it is preferable that the plug 53 be shieldedas at 59, the shield 59 being connected to a sleeve contact 60 of theplug which is grounded at 40 through the Contact 39 of the jack.

With particular reference to Fig. 2, a vacuum amplifier tube 6I isconnected in the amplifier stage I4 and includes an anode 62, a cathodeE3, a control grid 64, a screen grid 65, a suppressor grid 66 and aheater 61. The heater 61 is energized from a secondary Winding 68 of atransformer 59, which transformer 69 is preferably enclosed in a shieldIIa. The control grid 64 is connected through a resistor 19 to an inputterminal or spring contact 1I of a' jack 12 and to one end of a gridresistor 13. The other end of the grid resistor 13 is connected to aninput terminal or spring contact 14 of the jack 12 and is preferablygrounded at 15. A battery 16 has a resistor 11 connected thereacrossthrough a switch 18 and has one end connected to the input terminal orcontact 14. A variable mid-tap 19 on the resistor 11 is connected to thecathode 63 so that the battery 16 provides a grid biasing potentialwhich is varied by varying the position of the mid-tap 19 on theresistor 11 when the switch 'I8 is closed. The suppressor grid 66 isconnected to the cathode 63. The anode 62 is connected through an anodeor plate resistor B9 to a contact or ring BI of a plug 82 and to avoltage divider comprising resistors 83 and 84.

The anode 62 is coupled to the succeeding amplifler stage I5 through acondenser 85 and a resistor 96. The amplifier stage I5 includes a vacuumamplifier tube 31, which has a control grid 88, a cathode 89, an anode9U, a screen grid 9I, a suppressor grid 92, and a heater 93. A battery94 has one terminal connected to the cathode 89 and the other terminalconnected to the control grid 88 through a grid resistor 95 and theseries resistor 66 to provide the biasing potential for the grid 88. Thesuppressor grid 92 is connected to the cathode 89. The heater 93 isenergized from the secondary winding 63 which also energizes the heater61 of the tube 6I. The anode 99 is connected to an output terininal ortip contact 96 of the plug 82. A sleeve |02 and |03. The primary winding|00 has leads |04 that are adapted to be connected to a source ofalternating current. The secondary winding |02, which is preferably ahigh voltage winding, has its ends connected to plates or anodes |95 and|06 of a rectifier tube |01. The filament or cathode |08 of therectifier tube is energized by the secondary winding |03. The secondarywinding |02 has a center tap |09 that is connected to voltage dividerresistors ||0 and and to an electrode ||2 of a gas discharge tube H3.The secondary winding |03 has a center tap ||4 that is connected throughan iron core choke coil ||5 to the anode ||6 of a vacuum regulator tube||1. Filter condensers ||8 and ||9 are connected to the ends of thechoke coil H5 and to the lead from the center tap |09 of the secondarywinding |02. The vacuum regulator tube ||1 includes, besides the anodeH6, a control grid |20 and a lament or cathode |2|. A regulator controltube |22 includes an anode |23, a control grid |24, a cathode |25, aheater |26, a screen grid |21, and a suppressor grid |28.

The voltage divider which includes the resistor also includes resistors|29 and |39 connected in series across the high voltage leads from thecenter taps |09 and ||4 of the secondary windings |02 and |03, Thevoltage divider which includes the resistor` ||0 also includes aresistor |3| connected in series therewith across the same high voltageleads. The cathode |25 and suppressor grid |28 of the control tube |22are connected together and to the common terminals of the voltagedivider resistors and |29 to establish the potential thereof. The screengrid |21 is connected to the common terminal of the voltage dividerresistors l0 and |3|. The heater |26 of the control tube |22 isenergized from the secondary winding 68. The potential of the controlgrid |24 of the control tube |22 is established by its connection to thecommon terminal of voltage divider resistors 33 and |34, which areconnected in series and to the center tap |09 of the secondary Windingand the ring or terminal 8| of the plug 62. A condenser !35 ispreferably connected across .the resistor |34.

The filament or cathode |2| of the regulator tube ||1 is energized fromthe secondary winding |9| and preferably has a tapped resistor |36connected thereacross to provide a mid-tap connection |31 to thefilament. The mid-tap connection |31 is connected to the ring 8| of theplug 32 and to one end of a resistor |38. The other end of the resistor|38 is connected to the control grid |20. A resistor |39 has one endconnected to the anode ||6 and the other end connected to the controlgrid |20.

An electrode |40 of the gas discharge tube H3 is connected to the commonterminal of the resistors |29 and |30, so that the gas discharge tube||3 is connected across the voltage divider resistors and |29. Aresistor |4| is preferably connected to the electrodes ||2 and |49 ofthe gas discharge tube.

A gas discharge tube |42 has electrodes |43 and |44. The electrode |43is connected to the center tap |09 of the secondary winding |02 and theelectrode |44 is connected to the screen grids 65 and 9| of theampliiier tubes 6| and 81, respectively. The gas discharge tube 42 isalso connected across the voltage divider resistor 04. The gas dischargetubes |42 and H3 each have break-down voltages somewhat below thevoltages applied thereto yand such that they act somewhat as variableirnpedances for regulating the voltages that are applied thereto.

With particular reference to Fig. 3, the amplier stage I6 includesvacuum amplifier tubes |46 yand |41. The tube |46 has an anode or plate|48, a grid |49 and a cathode or lament |50. The tube |41 has an anodeor plate |5|, a control grid |52 and a cathode or lament |53. Thecontrol grids |49 and |52 are connected through grid coupling resistors|54 and |55 that are connected in series. The grid |49 is also connectedto one side of a coupling condenser |56, the other side of whichcondenser is con' nected to one end of a resistor |51 and to an inputterminal or contact |58. The grid |52 is connected to one side of acoupling condenser |59 and the other side of the condenser |59 isconnected to the other end of the resistor |51 and to an input terminalor contact |60. The input lterminals or contacts |58 and |65 arepreferably contacts of a jack |6| and engage the tip 96 and ring 8|,respectively, of the plug 82. The resistor |51 is the plate resistor forthe amplifier tube 81 and is preferably placed in the section shown inFig. 3 to shorten the leads which extend therefrom to the control grids|49 and |52. YA grid bias resistor |62 has one end grounded art |63 andconnected to the common terminal of the resistors |54 and |55. Thelaments or cathodes |50 and |53 are connected in parallel and areenergized from a secondary winding |64 of a transformer 65. Thesecondary winding'l64 is preferably provided with a center tap at |66,which is connected to the other end of the grid biasing resistor |62.

The transformer |65 has a primary Winding |01 and secondary windings|68, |69, |10 and |1|, in addition to the secondary winding |64. Leads|12, that are connected to the ends ofthe primary Winding |61, areadapted to connect the primary winding to a suitable source ofalternating current. The ends of the secondary winding |69 are connectedto ancdes or plates |13 and |14 of a rectifier tube |15. The rectifiertube |15 has a cathode or lament |16 that is energized from thesecondary winding |60. `A center tap 11 on the secondary winding |69 isconnected to the common terminal of the resisters |54 and |55 and to acontact |18 of the jack |6|, which contact |18 engages the sleeve 91 ofthe plug 82. A centervtap |90 on the secondary winding |68 is connectedthrough iron core choke coils |8| and |82 to a variable tap |83 on aresistor |84. Filter condensers |85 and |86 are connected to the ends ofthe choke coil |82 and to ground at |81 and |88, respectively, to assistthe choke coils |8| and |82 in ltering the current rectified by therectiiier tube |15. The ends of the resistor |84 are connected throughjack switches |09 and |90 to anodes |9| and |92 of voltage regulatortubes |93 and |94, respectively.

The voltage regulator tube |93 has a control grid |95 that is lconnectedto the anode |48 of the amplifier tube |46, and also has a larnent orcathode |96 that is connected across the sec ondary winding |1'0. Thevoltage regulator tube |94 has a control grid |91 that is yconnected toa resistor 292 to the anode |5l. Rectified plate current from the centertap |88 of the secondary winding |63 iiows through the choke coils |8|and |82, resistor |84, voltage regulator tubes |93 and |94, andresistors 299 and 252, respectively, to the anodes or plates I 48 and|5|. The jack switches |89 and |90 are preferably provided in thecircuits of the anodes |9| and |52 for making the connections to a meterfor measuring the anode currents to the voltage regulator tubes |93 and|94.

Output terminals 263 and 294 are provided for making connections to asuitable reproducer or recorder which constitutes a load on theamplifying system. The terminal 294 is connected to the anode or plateI5| of the amplifier tube |41 through the resistor 292. The outputterminal 293 is connected to one side of a switch 291 and to one side ofa meter or indicating device 258. The meter 288 is preferably one of thecenter zero type which will deflect in either direction depending uponthe direction of current flow therethrough. The other side of the switch281 is connected to the other side of the meter or indicating device 298and to one end of the resistor 296, so that when the switch 281 isclosed the meter or indicating device is shunted out of the circuit. Oneend of the resistor 266 is also connected to a variable tap 295 whichcontacts the resistor, so that a variable portion of the resistor 296 isshort-circuited to vary the effective sensitivity of the meter. Theother end of the resistor 296 is connected to the resistor 259 and tothe center tap |99 of the secondary winding |19. The reproducing deviceor recorder that is connected to the output terminals 283 and 284 completes a circuit between those terminals.

In the operation oi the amplifying system of my invention, which isdisclosed herein, the signal or impulse to be amplified is applied tothe control grids 2| and 22 of the amplier tubes l1 and I8 through theleads 56 and 51. In the case of amplifying impulses or waves from somepart of the human anatomy, such as those from different parts of thehead, suitable electrodes are connected to the leads 56 and 51 andsecured to the anatomy. It is particularly important to prevent thepicking up of any stray impulses in the input leads which would beamplified along with the impulses that are actually desired andutilized. The input leads are covered by a shield 58 and are alsoshielded by the shield 59 within the plug 53 to prevent the picking upof such stray impulses.

By utilizing heater type tubes l1 and i8 which do not quickly respond tovariations in heater temperature, alternating current can be utilized toheat the heaters 21 and 23 and the cathodes 25 and 26. However, sincethe impulses from the first stage of the amplifying system arearnplifled considerably, it is preferable to utilize batteries 41 and 49for providing the grid biasing, screen grid and anode potentials,because the batteries provide perfectly steady potentials which do notintroduce any disturbing impulses. As another precaution against theintroduction of stray impulses, the transformer 29 is preferablyindividually shielded from the rest of the plied to the amplier.

and 14, respectively, of the jack 12. The impulses or Waves are ampliedin the second section, shown in Fig. 2, by the amplifier stagesincluding the tubes 6| and 81 which are connected in cascade. Theampliiied impulses from the tube 81 are applied to the third section ofthe amplifier which is shown in Fig. 3 through the connections providedbetween the sleeve 82 and contact |6| and between the tip 96 and thecontact |58. The additional contact |69 on the jack |6| and thecooperating ring contact 8| are necessary because the plate resistor |51is preferably placed close to the grids |49 and |52 and the plate oranode potential for the anode or plate 99 is obtained from the cathodeor filament |2| of the regulator tube ||1 through the mid tap |31 of theresistor |36. This potential is applied to the anode 99 through theresistor |51.

The load or reproducer which preferably comprises a recording device isconnected to the terminals 293 and 294 to complete the circuit betweenthose terminals and between the anodes |48 and |5|. The recording device(not shown) may be a loud speaker reproducing element with a pen mountedthereon to trace the reproduced wave forms on a moving paper tape whenthe device is used to amplify impulses, such as those from parts of theanatomy.

When the amplier is turned on, the section shown in Fig. 3, whichconstitutes the last stage thereof, is preferably turned on before theother stages; then with only the third section turned on the variabletap 295 on the resistor 296 is adjusted to a position such that theeffective sensitivity of the meter or indicating device is reduced. Thevariable tap |83 on the resistor |84 is adjusted to a position such thatthe meter 29S reads zero, even when the sensitivity thereof is increasedby adjustment of tap 295. This balances the voltage on the amplifiertubes |46 and |41. After the adjustment of the variable tap |83, theother stages are turned on and the position of the variable tap on theresistor 35 is adjusted so that the meter or indicating device 268 isagain set at its center zero position. This latter adjustment adjuststhe signal input to and the operation of the amplifier tubes l1 and I8.Any deflection of the meter 298 which is not balanced out by adjustmentof the taps |83 and 59 on resistors |84 and 35 shows the presence ofoscillations or some unbalanced condition in the amplier,

The previously described adjustments are made without having any signalor impulses ap- After these adjustments are made the switch 281 isclosed to shunt the meter or indicating device 298 from the circuit.When the signals or impulses to be amplified are applied through theleads 56 and 51, the variable tap 19 on the resistor 11 is adjusteduntil the desired amplitude is obtained on the reproducer or recordingdevice that is connected to the output terminals 293 and 294.

Since it adds to the portability and convenience of the apparatus toutilize alternating current wherever possible as a source of power,transformers and rectiers have been utilized in the second and thirdsections, shown in Figs. 2 and 3, to provide the power for energizingthe cathodes and anodes of the ampler tubes. To avoid the introductionof variations in the output due to fluctuations of voltage on theamplier tubes, the second and third sections have each been providedwith voltage regulators.

In the second section, shown in Fig, 2, the gas discharge tube H3provides a partial regulation of the high voltage direct current, andthe regulator tube 98, which is at least partially controlled by thecontrol tube |22, provides a more precise regulation of the rectifieddirect current potentials. The positive side of the rectied current isconnected to the anode ||6 of the regulator utbe 98 from the center tap||4 of the secondary winding |33. This current iiows through theregulator tube 98 to the cathode |2| thereof and to the anodes 62 and 9@of the anipliier tubes. Since the potential of the control grid |24 ofthe control tube |22 is dependent upon the potential of the cathode |2|of the regulator tube, and the potential of the control grid |20 of theregulator tube is controlled by and directly connected to the anode |23of the control tube, the control tube serves as a controlling element tocontrol the operation of the regulator tube. Although the potential ofthe control grid |24 is actually positive, it is below the potential ofthe cathode |25, so that it is actually negative with respect to thecathode.

It has been found that the resistors |38 and |39, which are respectivelyconnected from the cathode 12| to the grid |29 and from the anode H6 tothe grid |23, stabilize and improve the operation of the regulator tube38. The resistance values of the resistors |33 and |39 are preferablyhigh.

In addition to the gas discharge tube H3 and the regulator tube 9S, asecond gas discharge tube |42 is connected across the resistor 84 tocontrol the voltage applied to the screen grids 35 and 9| and improvethe operation and stability of the amplifier tubes 6| and 81. Thebreak-down voltage of the gas discharge tubes |13 and |42 is preferablybelow the normal voltage applied thereto, so that the tubes continuallyglow during normal operation. The resistor |4| that is connected acrossthe gas discharge tube H3 controls the voltage applied across that gasdischarge tube.

In the voltage regulating system utilized in the third section of theamplifier, which is shown in Fig. 3, the potential is applied to theanode |43 through the resistor 28|) and the regulator tube |93, sinceone end of the resistor Zilli is connected to the center tap |39 of thesecondary winding |10, and the anode |9| of the regulator tube isconnected through a portion of the resistor |84, and the choke coils |8|and |82 to the center tap |83 of the secondary winding |68. The anode |Iof the amplifier tube |41 has its potential applied thereto in a similarmanner through the resistor 2512 and the regulator tube |94. Theresistors 23|] and 232 preferably have low resistance values andestablish the grid biasing potentials of the grids |95 and |31 of thetubes |33 and |94 respectively, by virtue of their respectiveconnections to cathodes |96 and |98 through windings |1 and |1|. Theaction of the regulator tube |93 is controlled by the potential of theanode |48, since the control grid |95 is connected to the anode |43. Theconnection of the anode |5I to the control grid |91 causes the action ofthe regulator tube |94 to be responsive to the potential of the anodeThe regulator tubes |93 and |94 thus tend to eliminate variations in thedirect current potentials applied to the anodes |48 and |5|,respectively. The potentials applied to the anodes |48 and |5| arebalanced by adjustment of the variable tap |83 on the resistor |84.

The resistors 10 and 86 in Fig. 2, which are respectively connected inseries with the control grids B4 and V88 of the amplifier tubes 6| and81, preferably have high resistance values and are utilized to preventoscillation of the amplifier tubes 6| and 81. Further to improve thestability of the amplifying stages shown inV Fig. 2, all of the voltagedividers are connected to a common ground; that is, an end of each ofthe resistors ||0, |33 and 84 is connected to ground at 15. When thethree sections of the amplifier shown in Figs. 1, 2 and 3 are connectedtogether, the shields I0, and I2 are also preferably connected togetherand connected to an earth ground, such as a water pipe. Then to preventthe pick-up of stray impulses through a person to which the inputelectrodes are applied, that person is preferably enclosed in a screenbooth shield and grounded.

While I have described this specic embodiment vof my invention, Icontemplate that many changes may be made thereover without departingfrom the scope or spirit of my invention.

I claim:

l. A high fidelity amplifying system comprising, in combination, amulti-stage vacuum tube audio frequency amplifier having a plurality ofsections, means individually shielding said sections to prevent pick-upof extraneous impulses, each of said sections including at least onehigh fidelity amplifier stage, means connecting the stages in the saidsections in cascade, individual power supply means for each of thesections, and voltage regulating means included in a pait of thesections for stabilizing some of the voltages utilized in the samesection therewith.

2. A high fidelity amplifying system comprising, in combination, amulti-stage vacuum tube audio frequency amplifier having a plurality ofsections, means individually shielding said sections to prevent pick-upof extraneous impulses, each of said sections including at least onehigh fidelity amplifier stage, shielded means connecting the stages inthe said sections in cascade, individual power supply means for each ofthe sections, and voltage regulating means included in a part of thesections for stabilizing some of the voltages utilized in the samesection therewith, said voltage regulating means including a pluralityof vacuum tube controlling elements.

3. A high fidelity amplifying system comprising, in combination, amulti-stage vacuum tube audio frequency amplifier having a plurality ofsections, means individually shielding said sections to prevent pick-upof extraneous impulses, each of said sections including at least onehighfidelity amplifier stage, means connecting the stages in the saidsections in cascade, individual power supply means for each of thesections, and voltage regulating means included in a part of thesections for stabilizing some of the voltages utilized in the samesection therewith, said voltage regulating means including a gasdischarge tube for effecting partial regulation of the voltage andvacuum tube means for effecting more precise regulation of the voltage.

4. A high fidelity amplifying system comprising, in combination, amulti-stage vacuum tube audio frequency ampliiier having a plurality ofsections, means individually shielding said sections to present pick-upof extraneous impulses, each of said sections including at least onehigh fidelity amplier stage, means connecting the stages in the saidsections in cascade, individual power supply means for each of thesections, and voltage regulating means included in a part of thesections for stabilizing some of the voltages utilized in the samesection therewith, said voltage regulating means including a gasdischarge tube for effecting partial regulation of the voltage and apair of cooperating vacuum tubes for effecting more precise regulationof the Voltage.

5. An amplifying system comprising, in combination, a multi-stage vacuumtube amplifier comprehending a plurality of shielded sections, a part ofsaid sections each including a single resistance coupled amplifier stageof the push-pull type and one of said sections including a plurality ofresistance coupled amplifier stages, each of which last m-entionedstages includes a vacuum tube having a control grid, a resistorconnected in series with the control grid of each of said vacuum tubes,separate power supply means for each of said sections, and meansconnecting the amplifier stages together.

6. An amplifying system comprising, in coinbination, a multi-stagevacuum tube amplifier comprehending a plurality of shielded sections, apart of said sections each including a single resistance coupledamplifier stage of the push-pull type and one of said sections includinga plurality of resistance coupled amplifier stages, each of which lastmentioned stages includes a vacuum tube having a control grid, aresistor connected in sei'ies with the control grid of each of saidvacuum tubes, separate power supply means for each of said sections, theseparate power supply means for a part of said sections eachcomprehending a transformer, a rectifier tube and means for regulatingdirect current potential from the rectifier tube, and means connectingthe amplier stages together.

7. An amplifying system comprising, in combination, a multi-stage vacuumtube amplifier comprehending a plurality of shielded sections, a part ofsaid sections each including a single resistance coupled amplifier stageof the pushpull type and one of said sections including a plurality ofresistance coupled amplifier stages, each of which last mentioned stagesincludes a vacuum tube having a control grid, a resistor connected inseries with the control grid of each of said vacuum tubes, separatepower supply means for each of said sections, the separate power supplymeans for a part of said sections each comprehending a transformer, arectifier tube and means including a plurality of vacuum tubes forregulating direct current potential from the rectifier tube, and meansconnecting the amplifier stages together.

8. An amplifying system comprising, in combination, a multi-stage vacuumtube amplifier comprehending a plurality of shielded sections, a part ofsaid sections each including a single resistance coupled amplifier stageof the push-pull type and one of said sections including a plurality ofresistance coupled amplier stages, each of which last mentioned stagesincludes a vacuum tube having a control grid, a resistor connected inseries with the control grid of each of said vacuum tubes, separatepower supply means for each of said sections, the separate power supplymeans for a part of said sections each comprehending a transformer, arectifier tube and means for regulating direct current potential fromthe rectifier tube, the means for regulating direct current potential inone of the sections comprising gas discharge tube means and a pair ofcooperating vacuum tubes, and means connecting the amplifier stagestogether.

9. In ari amplifying system, the lcombination comprising an amplifierstage of the push-pull type including two vacuum tubes having anodes, asource of direct current, and means for regulating the potential appliedto the anodes, said means comprehending a vacuum tube connected inseries with and between each of the anodes and the source of potential,the last mentioned vacuum tubes having control grids, and the potentialsof each of said control grids being determined by the potential of oneof the anodes.

10. In an amplifying system, the combination comprising an amplifierstage including an amplier tube having an anode, a source of anodepotential for the said anode, and means for regulating the potentialapplied to the anode, said means comprehending a regulator tube having acontrol grid, an anode and a cathode, the anode of the regulator tubebeing connected to said source, said cathode being connected to theanode of the amplifier tube, and the anode of the amplifier tube beingconnected to the control grid of the regulator tube so that theregulator tube is responsive to the potential of the anode of theamplifier tube.

VICTGR MISTRO.

